1. Field of the Invention
The present invention relates to an image capturing device.
2. Description of the Related Art
A complementary metal-oxide semiconductor (CMOS) is available as one kind of image sensor used for image input in an electronic device (for example, a copier or a facsimile). A CMOS image sensor amplifies a signal from a pixel through a programmable-gain amplifier (PGA), performs analog-to-digital (AD) conversion on the amplified signal through an analog-to-digital converter (ADC), and outputs the resultant digital signal. Each unit, such as each pixel or each column in a pixel array, needs to be provided with such a PGA and an ADC. A pixel pitch is as narrow as several micrometers. For this reason, when such circuits are integrated on chips, the areas occupied thereby need to be as small as possible so as to be within the pitch width. One technique often employed in effort to satisfy this need is employment of a ramp ADC or a cyclic ADC as an ADC.
There is a document that discloses an invention aimed at obtaining a gain through a PGA in a CMOS image sensor. The document discloses a technique that: segments an output signal of correlated double sampling (CDS) into a plurality of regions in accordance with the intensity of the signal; and amplifies each segmented region of the signal through the PGA with a gain set for the each region (refer to Japanese Unexamined Patent Application Publication No. 2010-41221).
However, a conventional configuration is accompanied by the need to enlarge the size of an element in an attempt to increase a gain of a PGA. Specifically in this case, since a PGA is not allowed to be within a pixel pitch (or an integer multiple of a pixel pitch), it is necessary to enlarge the area occupied by the PGA in a column-wise direction perpendicular to the pixel pitch. The conventional configuration thus has a disadvantage such that an attempt to obtain a high gain of a PGA inevitably involves increase in circuit area thereof.